This invention relates generally to a cardiac rhythm management device capable of determining whether a stimulus delivered to a patient""s heart evokes a response. More particularly, this invention relates to a method and device for delivering stimulation pulses to pre-determined chambers within an electrically continuous area of the patient""s heart and then determining independently for each stimulation pulse whether the stimulus evokes a response or is xe2x80x9ccapturedxe2x80x9d by the corresponding cardiac muscle. The independent determination of capture for each chamber of the patient""s heart may be activated via telemetry or by applying a magnetic field proximate the device. The capture verification may be performed manually by a physician utilizing telemetry or may be performed automatically by the device. During the capture verification mode of the present invention, bi-chamber stimulation may precede or follow uni-chamber stimulation to allow for stimulation support during the capture verification mode.
Cardiac stimulators typically include a pulse generator, limited power supply, electrical leads coupled thereto, and a controller. The controller typically includes a microprocessor having preprogrammed code, and may include ROM memory for storing programs to be executed by the controller and RAM memory for storing operands used in carrying out the computations by the controller. In order to maximize use of the limited power supply, it is desirable to set the pulse generator""s stimulation output at the lowest output energy that reliably causes depolarization of the corresponding cardiac muscle.
To ensure the reliability of xe2x80x9ccapturingxe2x80x9d a stimulation such as a pacing pulse, it is common practice to determine the minimum output energy that induces a cardiac depolarization (xe2x80x9cthe energy thresholdxe2x80x9d) manually during patient follow-ups, and then set the pacing pulse output at this minimum setting plus a wide error margin, oftentimes double or triple the minimum effective energy. This error margin is meant to account for the changes in energy requirements that may occur over time between patient follow-ups. Typically, when determining the energy threshold of the ventricles, both ventricles are simultaneously stimulated and if depolarization is detected, capture of both ventricles is assumed. It is expected to be far more efficient and/or economic for a pacemaker to determine a threshold for each chamber independently and adjust the output energy settings independently thereby incorporating a much smaller error margin.
For example, oftentimes a cardiac rhythm management device utilized for treating congestive heart failure delivers stimulation therapy to both sides of the heart for either atrial stimulation or ventricular stimulation. The sensing for depolarization signals from the corresponding chambers is non-discriminatory, such that if a depolarization signal is sensed, the device assumes capture in both chambers. The false assumption that the capture threshold is the same in both chambers may reduce the effectiveness of the stimulation therapy. Hence, there is a need for a device that verifies capture independently for stimulation pulses delivered to pre-determined chambers within an electrically continuous area of the patient""s heart. The present invention meets these and other needs that will become apparent from a review of the description of the present invention.
The present invention provides a method and apparatus that may be used, for example, to treat congestive heart failure in a patient. The method and device of the present invention provides for the physician a mechanism for determining whether a stimulation to each pre-selected chamber evokes a response. The cardiac rhythm management device of the present invention generally includes a pulse generator, power supply, controller, leads coupled thereto, and a linkage of known suitable construction to provide for telemetry between the device and an external programmer. The cardiac rhythm management device of the present invention may include a stimulation means for transmitting at least first and second stimulation pulses during a cardiac cycle to an electrically continuous area of the heart, a sensing means for sensing a response to each stimulation pulse, and a controller connected to the stimulation means and sensing means, wherein the controller includes a mode for determining whether each stimulation results in capture.
The mode for determining whether each stimulation output results in capture may be activated by an externally applied magnetic field or may be activated by the physician/programmer via telemetry. The cardiac rhythm management device of the present invention provides uni-chamber stimulation and allows verification of capture for each uni-chamber stimulation. In one embodiment of the present invention, a first stimulation is directed to a right ventricle of the patient and a second stimulation is directed to a left ventricle of the patient. Capture is then determined separately for the left and right ventricle. In another embodiment of the present invention, the first stimulation is directed to the right atrium of the patient and the second stimulation is directed to the left atrium of the patient. Capture is then determined independently for the left and right atrium. In still another embodiment of the present invention, the first stimulation may be directed to a first pre-selected chamber at a first pre-selected site of the patient""s heart and the second stimulation may be directed to the same pre-selected chamber at a second pre-selected site of the patient""s heart. Those skilled in the art will appreciate that other stimulation sequences may be applied to the atriums or ventricles and then capture may be determined independently in accordance with the present invention.
When the capture verification mode is activated, several first stimulation pulses may be transmitted to the heart prior to transmitting the second stimulation pulses. Those skilled in the art will appreciate that xe2x80x9cnormalxe2x80x9d stimulation pulses or stimulation pulses known to evoke a response may be applied between transmitting the first stimulation pulses and the second stimulation pulses. Application of normal stimulation pulses between the first and second stimulation pulses in affect neutralize any affects the first stimulation may have on the effectiveness of the second stimulation pulses. Further, application of the normal stimulation pulses between the first and second stimulation pulses may provide the patient with pacing therapy if the test pulses did not capture the heart. Also, the stimulation energy of the stimulation pulses may be varied by a predetermined amount to further identify the minimum required energy required to evoke a response by the heart.
In use, the preferred method for verifying capture of stimulation pulses delivered to pre-selected chambers of a patient""s heart includes the following steps: activating an algorithm or predetermined parameters of the cardiac rhythm management device via a magnetic field of prescribed strength and duration or other external device; delivering during a cardiac cycle first and second stimulation pulses to an electrically continuous area of the heart in accordance with the algorithm or preset parameters; sensing and monitoring the depolarization waveforms corresponding to each stimulation pulse; and determining whether each stimulation results in capture. The preferred method utilizes a means for sensing cardiac electrogram signals, a programmable controller coupled to receive signals from an external programmer, a telemetry link, an external depolarization monitor and stimulation means for applying cardiac stimulation pulses to a patient""s heart in accordance with the timing and energy output determined by the physician or user. The controller may include means for controlling both the pulse generator and the stimulation output generated by the pulse generator, means for determining intrinsic heart cycle lengths, and means for analyzing signals sensed by one or more electrodes after a pre-selected time expires after transmitting a stimulation pulse to another electrode.
Hence, the cardiac rhythm management device of the present invention is capable of allowing independent verification of capture for each ventricle or atrium of the heart. The cardiac rhythm management device includes a capture verification mode that may be activated by applying a magnetic field proximate the device, wherein the capture verification may be controlled via telemetry. Also, the cardiac rhythm management device is capable of delivering stimulation pulses to pre-determined chambers within an electrically continuous area of the patient""s heart and thereafter allows independent verification of capture for each stimulation. Also, the cardiac rhythm management device is capable of transmitting xe2x80x9cnormalxe2x80x9d stimulation pulses at predetermined intervals during the capture verification mode. These and other advantages of the present invention will become readily apparent to those skilled in the art from a review of the following detailed description of the preferred embodiment especially when considered in conjunction with the claims and accompanying drawings in which like numerals in the several views refer to corresponding parts.